1. Field of the Invention
The present invention relates to whiskers-containing fiber-reinforced ceramics and, more particularly, relates to such ceramics with high fracture toughness that is particularly suitable for use as cutting tools and other abrasion resistant parts, and the process of production thereof.
2. Description of the Prior Art
While sintered bodies produced from alumina (Al.sub.2 O.sub.3) are utilized as materials excelling in abrasion resistance for various industrial machine parts, its applicable field has been kept from expanding because of its shortcoming of inferior fracture toughness.
In view of the aforementioned circumstance, there have been various proposals aimed at improved fracture toughness.
As one example of the aforementioned proposals, there has been proposed in Japanese Laid-Open Application Sho 61-286271 and Japanese Laid-Open Application Sho 62-41776 certain means of improving fracture toughness by blending a fibrous material represented by silicon carbide whiskers.
Such a ceramic material reinforced by the incorporation of fibers containing SiC whiskers exhibits excellent performance properties in cutting certain ultra-heat resistant alloys (e.g. roughing cut on Inconel 718) when it is used as a cutting tool, since SiC by itself has high hardness and good heat conductivity.
Nevertheless, since SiC tends to readily react with iron, particularly iron oxides, Al.sub.2 O.sub.3 --SiC whiskers-based tools in many cases tend to wear off at a higher rate than tools consisting principally of Al.sub.2 O.sub.3. For example, when a material constructed of SUS 304 is worked on for cutting, the tool containing SiC whiskers gives rise to a problem that cutting is practically impossible to perform due to the rapid progress of wear even under comparable conditions which would sufficiently enable the conventional Al.sub.2 O.sub.3 tool to accomplish cutting. Besides, it has been verified that the wear rate of Al.sub.2 O.sub.3 --SiC whiskers-containing tool is higher than that of Al.sub.2 O.sub.3 tool in cutting cast iron-made stock material.
As stated above, the Al.sub.2 O.sub.3 --Sic whiskers-containing tool poses a problem that cutting properties notably vary with the material to work on.
Meanwhile, there has been recently proposed the incorporation of titanium carbide (TIC) whiskers, which have a lower reactivity with iron than SiC, instead of SiC whiskers, for the purpose of eliminating such reactivity with the ferrous material worked on.
Nevertheless, in the case of Al.sub.2 O.sub.3 --TiC material, its strength tends to decrease, since the particle size of alumina increases due to the grain growth of alumina in the sintering step which is excessively high. As for the cause of excessively high grain growth of Al.sub.2 O.sub.3 in the sintering step, it is inferred firstly that the difficulty with the preparation of fine, uniform TiC whiskers restrains the inherent effect of the whiskers to inhibit the grain growth of alumina only to a low level, and secondly that TiO.sub.2 produced by oxidation of TiC whiskers on their surfaces accelerates the grain growth of Al.sub.2 O.sub.3.
Ordinarily, mechanical properties of the alumina-based sintered body to a large extent depend upon the particle size of alumina crystal in the sintered body, and it is said that the smaller the particle size, the higher becomes its strength.
Hence, under the present circumstance, the conventional Al.sub.2 O.sub.3 --Tic whiskers-containing material properties are not upgraded to an extent that such material is rendered practically useful.